The use of extruded thermoplastics for window construction offers numerous advantages. It can be extruded in intricate shapes. Provided suitable thermoplastic material is selected, it can be made strong, and weatherproof, and having an attractive finish not requiring any maintenance. These advantages have been known for many years. Various proposals have been made for employing extruded thermoplastics in windows. A common problem has been a tendency for the material to warp, leading to an unsatisfactory seal around the window. Another problem has been the difficulty of anchoring the window frame to a building structure. Other problems have arisen in that in some cases, the thermoplastic did not offer sufficient support to the window glazing.
Another problem frequently encountered in the past was in the area of security. Thermoplastic extruded windows in many cases did not offer a satisfactory solution to the problem of building security, and in some cases could be opened with relative ease.
Clearly, it is desirable for a thermoplastic window construction to have strength and rigidity and security at least equal to that of conventional metal window designs, without the disadvantages of metal window design particularly in cold climates.